1 /* 2 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.util; 27 28 import java.lang.ref.WeakReference; 29 import java.lang.ref.ReferenceQueue; 30 import java.util.concurrent.ThreadLocalRandom; 31 import java.util.function.Consumer; 32 33 34 /** 35 * Hash table based implementation of the <tt>Map</tt> interface, with 36 * <em>weak keys</em>. 37 * An entry in a <tt>WeakHashMap</tt> will automatically be removed when 38 * its key is no longer in ordinary use. More precisely, the presence of a 39 * mapping for a given key will not prevent the key from being discarded by the 40 * garbage collector, that is, made finalizable, finalized, and then reclaimed. 41 * When a key has been discarded its entry is effectively removed from the map, 42 * so this class behaves somewhat differently from other <tt>Map</tt> 43 * implementations. 44 * 45 * <p> Both null values and the null key are supported. This class has 46 * performance characteristics similar to those of the <tt>HashMap</tt> 47 * class, and has the same efficiency parameters of <em>initial capacity</em> 48 * and <em>load factor</em>. 49 * 50 * <p> Like most collection classes, this class is not synchronized. 51 * A synchronized <tt>WeakHashMap</tt> may be constructed using the 52 * {@link Collections#synchronizedMap Collections.synchronizedMap} 53 * method. 54 * 55 * <p> This class is intended primarily for use with key objects whose 56 * <tt>equals</tt> methods test for object identity using the 57 * <tt>==</tt> operator. Once such a key is discarded it can never be 58 * recreated, so it is impossible to do a lookup of that key in a 59 * <tt>WeakHashMap</tt> at some later time and be surprised that its entry 60 * has been removed. This class will work perfectly well with key objects 61 * whose <tt>equals</tt> methods are not based upon object identity, such 62 * as <tt>String</tt> instances. With such recreatable key objects, 63 * however, the automatic removal of <tt>WeakHashMap</tt> entries whose 64 * keys have been discarded may prove to be confusing. 65 * 66 * <p> The behavior of the <tt>WeakHashMap</tt> class depends in part upon 67 * the actions of the garbage collector, so several familiar (though not 68 * required) <tt>Map</tt> invariants do not hold for this class. Because 69 * the garbage collector may discard keys at any time, a 70 * <tt>WeakHashMap</tt> may behave as though an unknown thread is silently 71 * removing entries. In particular, even if you synchronize on a 72 * <tt>WeakHashMap</tt> instance and invoke none of its mutator methods, it 73 * is possible for the <tt>size</tt> method to return smaller values over 74 * time, for the <tt>isEmpty</tt> method to return <tt>false</tt> and 75 * then <tt>true</tt>, for the <tt>containsKey</tt> method to return 76 * <tt>true</tt> and later <tt>false</tt> for a given key, for the 77 * <tt>get</tt> method to return a value for a given key but later return 78 * <tt>null</tt>, for the <tt>put</tt> method to return 79 * <tt>null</tt> and the <tt>remove</tt> method to return 80 * <tt>false</tt> for a key that previously appeared to be in the map, and 81 * for successive examinations of the key set, the value collection, and 82 * the entry set to yield successively smaller numbers of elements. 83 * 84 * <p> Each key object in a <tt>WeakHashMap</tt> is stored indirectly as 85 * the referent of a weak reference. Therefore a key will automatically be 86 * removed only after the weak references to it, both inside and outside of the 87 * map, have been cleared by the garbage collector. 88 * 89 * <p> <strong>Implementation note:</strong> The value objects in a 90 * <tt>WeakHashMap</tt> are held by ordinary strong references. Thus care 91 * should be taken to ensure that value objects do not strongly refer to their 92 * own keys, either directly or indirectly, since that will prevent the keys 93 * from being discarded. Note that a value object may refer indirectly to its 94 * key via the <tt>WeakHashMap</tt> itself; that is, a value object may 95 * strongly refer to some other key object whose associated value object, in 96 * turn, strongly refers to the key of the first value object. If the values 97 * in the map do not rely on the map holding strong references to them, one way 98 * to deal with this is to wrap values themselves within 99 * <tt>WeakReferences</tt> before 100 * inserting, as in: <tt>m.put(key, new WeakReference(value))</tt>, 101 * and then unwrapping upon each <tt>get</tt>. 102 * 103 * <p>The iterators returned by the <tt>iterator</tt> method of the collections 104 * returned by all of this class's "collection view methods" are 105 * <i>fail-fast</i>: if the map is structurally modified at any time after the 106 * iterator is created, in any way except through the iterator's own 107 * <tt>remove</tt> method, the iterator will throw a {@link 108 * ConcurrentModificationException}. Thus, in the face of concurrent 109 * modification, the iterator fails quickly and cleanly, rather than risking 110 * arbitrary, non-deterministic behavior at an undetermined time in the future. 111 * 112 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 113 * as it is, generally speaking, impossible to make any hard guarantees in the 114 * presence of unsynchronized concurrent modification. Fail-fast iterators 115 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 116 * Therefore, it would be wrong to write a program that depended on this 117 * exception for its correctness: <i>the fail-fast behavior of iterators 118 * should be used only to detect bugs.</i> 119 * 120 * <p>This class is a member of the 121 * <a href="{@docRoot}/../technotes/guides/collections/index.html"> 122 * Java Collections Framework</a>. 123 * 124 * @param <K> the type of keys maintained by this map 125 * @param <V> the type of mapped values 126 * 127 * @author Doug Lea 128 * @author Josh Bloch 129 * @author Mark Reinhold 130 * @since 1.2 131 * @see java.util.HashMap 132 * @see java.lang.ref.WeakReference 133 */ 134 public class WeakHashMap<K,V> 135 extends AbstractMap<K,V> 136 implements Map<K,V> { 137 138 /** 139 * The default initial capacity -- MUST be a power of two. 140 */ 141 private static final int DEFAULT_INITIAL_CAPACITY = 16; 142 143 /** 144 * The maximum capacity, used if a higher value is implicitly specified 145 * by either of the constructors with arguments. 146 * MUST be a power of two <= 1<<30. 147 */ 148 private static final int MAXIMUM_CAPACITY = 1 << 30; 149 150 /** 151 * The load factor used when none specified in constructor. 152 */ 153 private static final float DEFAULT_LOAD_FACTOR = 0.75f; 154 155 /** 156 * The table, resized as necessary. Length MUST Always be a power of two. 157 */ 158 Entry<K,V>[] table; 159 160 /** 161 * The number of key-value mappings contained in this weak hash map. 162 */ 163 private int size; 164 165 /** 166 * The next size value at which to resize (capacity * load factor). 167 */ 168 private int threshold; 169 170 /** 171 * The load factor for the hash table. 172 */ 173 private final float loadFactor; 174 175 /** 176 * Reference queue for cleared WeakEntries 177 */ 178 private final ReferenceQueue<Object> queue = new ReferenceQueue<>(); 179 180 /** 181 * The number of times this WeakHashMap has been structurally modified. 182 * Structural modifications are those that change the number of 183 * mappings in the map or otherwise modify its internal structure 184 * (e.g., rehash). This field is used to make iterators on 185 * Collection-views of the map fail-fast. 186 * 187 * @see ConcurrentModificationException 188 */ 189 int modCount; 190 191 private static class Holder { 192 static final boolean USE_HASHSEED; 193 194 static { 195 String hashSeedProp = java.security.AccessController.doPrivileged( 196 new sun.security.action.GetPropertyAction( 197 "jdk.map.useRandomSeed")); 198 boolean localBool = (null != hashSeedProp) 199 ? Boolean.parseBoolean(hashSeedProp) : false; 200 USE_HASHSEED = localBool; 201 } 202 } 203 204 /** 205 * A randomizing value associated with this instance that is applied to 206 * hash code of keys to make hash collisions harder to find. 207 * 208 * Non-final so it can be set lazily, but be sure not to set more than once. 209 */ 210 transient int hashSeed; 211 212 /** 213 * Initialize the hashing mask value. 214 */ 215 final void initHashSeed() { 216 if (sun.misc.VM.isBooted() && Holder.USE_HASHSEED) { 217 // Do not set hashSeed more than once! 218 // assert hashSeed == 0; 219 int seed = ThreadLocalRandom.current().nextInt(); 220 hashSeed = (seed != 0) ? seed : 1; 221 } 222 } 223 224 @SuppressWarnings("unchecked") 225 private Entry<K,V>[] newTable(int n) { 226 return (Entry<K,V>[]) new Entry<?,?>[n]; 227 } 228 229 /** 230 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial 231 * capacity and the given load factor. 232 * 233 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> 234 * @param loadFactor The load factor of the <tt>WeakHashMap</tt> 235 * @throws IllegalArgumentException if the initial capacity is negative, 236 * or if the load factor is nonpositive. 237 */ 238 public WeakHashMap(int initialCapacity, float loadFactor) { 239 if (initialCapacity < 0) 240 throw new IllegalArgumentException("Illegal Initial Capacity: "+ 241 initialCapacity); 242 if (initialCapacity > MAXIMUM_CAPACITY) 243 initialCapacity = MAXIMUM_CAPACITY; 244 245 if (loadFactor <= 0 || Float.isNaN(loadFactor)) 246 throw new IllegalArgumentException("Illegal Load factor: "+ 247 loadFactor); 248 int capacity = 1; 249 while (capacity < initialCapacity) 250 capacity <<= 1; 251 table = newTable(capacity); 252 this.loadFactor = loadFactor; 253 threshold = (int)(capacity * loadFactor); 254 initHashSeed(); 255 } 256 257 /** 258 * Constructs a new, empty <tt>WeakHashMap</tt> with the given initial 259 * capacity and the default load factor (0.75). 260 * 261 * @param initialCapacity The initial capacity of the <tt>WeakHashMap</tt> 262 * @throws IllegalArgumentException if the initial capacity is negative 263 */ 264 public WeakHashMap(int initialCapacity) { 265 this(initialCapacity, DEFAULT_LOAD_FACTOR); 266 } 267 268 /** 269 * Constructs a new, empty <tt>WeakHashMap</tt> with the default initial 270 * capacity (16) and load factor (0.75). 271 */ 272 public WeakHashMap() { 273 this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR); 274 } 275 276 /** 277 * Constructs a new <tt>WeakHashMap</tt> with the same mappings as the 278 * specified map. The <tt>WeakHashMap</tt> is created with the default 279 * load factor (0.75) and an initial capacity sufficient to hold the 280 * mappings in the specified map. 281 * 282 * @param m the map whose mappings are to be placed in this map 283 * @throws NullPointerException if the specified map is null 284 * @since 1.3 285 */ 286 public WeakHashMap(Map<? extends K, ? extends V> m) { 287 this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, 288 DEFAULT_INITIAL_CAPACITY), 289 DEFAULT_LOAD_FACTOR); 290 putAll(m); 291 } 292 293 // internal utilities 294 295 /** 296 * Value representing null keys inside tables. 297 */ 298 private static final Object NULL_KEY = new Object(); 299 300 /** 301 * Use NULL_KEY for key if it is null. 302 */ 303 private static Object maskNull(Object key) { 304 return (key == null) ? NULL_KEY : key; 305 } 306 307 /** 308 * Returns internal representation of null key back to caller as null. 309 */ 310 static Object unmaskNull(Object key) { 311 return (key == NULL_KEY) ? null : key; 312 } 313 314 /** 315 * Checks for equality of non-null reference x and possibly-null y. By 316 * default uses Object.equals. 317 */ 318 private static boolean eq(Object x, Object y) { 319 return x == y || x.equals(y); 320 } 321 322 /** 323 * Retrieve object hash code and applies a supplemental hash function to the 324 * result hash, which defends against poor quality hash functions. This is 325 * critical because HashMap uses power-of-two length hash tables, that 326 * otherwise encounter collisions for hashCodes that do not differ 327 * in lower bits. 328 */ 329 final int hash(Object k) { 330 int h = hashSeed ^ k.hashCode(); 331 332 // This function ensures that hashCodes that differ only by 333 // constant multiples at each bit position have a bounded 334 // number of collisions (approximately 8 at default load factor). 335 h ^= (h >>> 20) ^ (h >>> 12); 336 return h ^ (h >>> 7) ^ (h >>> 4); 337 } 338 339 /** 340 * Returns index for hash code h. 341 */ 342 private static int indexFor(int h, int length) { 343 return h & (length-1); 344 } 345 346 /** 347 * Expunges stale entries from the table. 348 */ 349 private void expungeStaleEntries() { 350 for (Object x; (x = queue.poll()) != null; ) { 351 synchronized (queue) { 352 @SuppressWarnings("unchecked") 353 Entry<K,V> e = (Entry<K,V>) x; 354 int i = indexFor(e.hash, table.length); 355 356 Entry<K,V> prev = table[i]; 357 Entry<K,V> p = prev; 358 while (p != null) { 359 Entry<K,V> next = p.next; 360 if (p == e) { 361 if (prev == e) 362 table[i] = next; 363 else 364 prev.next = next; 365 // Must not null out e.next; 366 // stale entries may be in use by a HashIterator 367 e.value = null; // Help GC 368 size--; 369 break; 370 } 371 prev = p; 372 p = next; 373 } 374 } 375 } 376 } 377 378 /** 379 * Returns the table after first expunging stale entries. 380 */ 381 private Entry<K,V>[] getTable() { 382 expungeStaleEntries(); 383 return table; 384 } 385 386 /** 387 * Returns the number of key-value mappings in this map. 388 * This result is a snapshot, and may not reflect unprocessed 389 * entries that will be removed before next attempted access 390 * because they are no longer referenced. 391 */ 392 public int size() { 393 if (size == 0) 394 return 0; 395 expungeStaleEntries(); 396 return size; 397 } 398 399 /** 400 * Returns <tt>true</tt> if this map contains no key-value mappings. 401 * This result is a snapshot, and may not reflect unprocessed 402 * entries that will be removed before next attempted access 403 * because they are no longer referenced. 404 */ 405 public boolean isEmpty() { 406 return size() == 0; 407 } 408 409 /** 410 * Returns the value to which the specified key is mapped, 411 * or {@code null} if this map contains no mapping for the key. 412 * 413 * <p>More formally, if this map contains a mapping from a key 414 * {@code k} to a value {@code v} such that {@code (key==null ? k==null : 415 * key.equals(k))}, then this method returns {@code v}; otherwise 416 * it returns {@code null}. (There can be at most one such mapping.) 417 * 418 * <p>A return value of {@code null} does not <i>necessarily</i> 419 * indicate that the map contains no mapping for the key; it's also 420 * possible that the map explicitly maps the key to {@code null}. 421 * The {@link #containsKey containsKey} operation may be used to 422 * distinguish these two cases. 423 * 424 * @see #put(Object, Object) 425 */ 426 public V get(Object key) { 427 Object k = maskNull(key); 428 int h = hash(k); 429 Entry<K,V>[] tab = getTable(); 430 int index = indexFor(h, tab.length); 431 Entry<K,V> e = tab[index]; 432 while (e != null) { 433 if (e.hash == h && eq(k, e.get())) 434 return e.value; 435 e = e.next; 436 } 437 return null; 438 } 439 440 /** 441 * Returns <tt>true</tt> if this map contains a mapping for the 442 * specified key. 443 * 444 * @param key The key whose presence in this map is to be tested 445 * @return <tt>true</tt> if there is a mapping for <tt>key</tt>; 446 * <tt>false</tt> otherwise 447 */ 448 public boolean containsKey(Object key) { 449 return getEntry(key) != null; 450 } 451 452 /** 453 * Returns the entry associated with the specified key in this map. 454 * Returns null if the map contains no mapping for this key. 455 */ 456 Entry<K,V> getEntry(Object key) { 457 Object k = maskNull(key); 458 int h = hash(k); 459 Entry<K,V>[] tab = getTable(); 460 int index = indexFor(h, tab.length); 461 Entry<K,V> e = tab[index]; 462 while (e != null && !(e.hash == h && eq(k, e.get()))) 463 e = e.next; 464 return e; 465 } 466 467 /** 468 * Associates the specified value with the specified key in this map. 469 * If the map previously contained a mapping for this key, the old 470 * value is replaced. 471 * 472 * @param key key with which the specified value is to be associated. 473 * @param value value to be associated with the specified key. 474 * @return the previous value associated with <tt>key</tt>, or 475 * <tt>null</tt> if there was no mapping for <tt>key</tt>. 476 * (A <tt>null</tt> return can also indicate that the map 477 * previously associated <tt>null</tt> with <tt>key</tt>.) 478 */ 479 public V put(K key, V value) { 480 Object k = maskNull(key); 481 int h = hash(k); 482 Entry<K,V>[] tab = getTable(); 483 int i = indexFor(h, tab.length); 484 485 for (Entry<K,V> e = tab[i]; e != null; e = e.next) { 486 if (h == e.hash && eq(k, e.get())) { 487 V oldValue = e.value; 488 if (value != oldValue) 489 e.value = value; 490 return oldValue; 491 } 492 } 493 494 modCount++; 495 Entry<K,V> e = tab[i]; 496 tab[i] = new Entry<>(k, value, queue, h, e); 497 if (++size >= threshold) 498 resize(tab.length * 2); 499 return null; 500 } 501 502 /** 503 * Rehashes the contents of this map into a new array with a 504 * larger capacity. This method is called automatically when the 505 * number of keys in this map reaches its threshold. 506 * 507 * If current capacity is MAXIMUM_CAPACITY, this method does not 508 * resize the map, but sets threshold to Integer.MAX_VALUE. 509 * This has the effect of preventing future calls. 510 * 511 * @param newCapacity the new capacity, MUST be a power of two; 512 * must be greater than current capacity unless current 513 * capacity is MAXIMUM_CAPACITY (in which case value 514 * is irrelevant). 515 */ 516 void resize(int newCapacity) { 517 Entry<K,V>[] oldTable = getTable(); 518 int oldCapacity = oldTable.length; 519 if (oldCapacity == MAXIMUM_CAPACITY) { 520 threshold = Integer.MAX_VALUE; 521 return; 522 } 523 524 Entry<K,V>[] newTable = newTable(newCapacity); 525 transfer(oldTable, newTable); 526 table = newTable; 527 528 /* 529 * If ignoring null elements and processing ref queue caused massive 530 * shrinkage, then restore old table. This should be rare, but avoids 531 * unbounded expansion of garbage-filled tables. 532 */ 533 if (size >= threshold / 2) { 534 threshold = (int)(newCapacity * loadFactor); 535 } else { 536 expungeStaleEntries(); 537 transfer(newTable, oldTable); 538 table = oldTable; 539 } 540 } 541 542 /** Transfers all entries from src to dest tables */ 543 private void transfer(Entry<K,V>[] src, Entry<K,V>[] dest) { 544 for (int j = 0; j < src.length; ++j) { 545 Entry<K,V> e = src[j]; 546 src[j] = null; 547 while (e != null) { 548 Entry<K,V> next = e.next; 549 Object key = e.get(); 550 if (key == null) { 551 e.next = null; // Help GC 552 e.value = null; // " " 553 size--; 554 } else { 555 int i = indexFor(e.hash, dest.length); 556 e.next = dest[i]; 557 dest[i] = e; 558 } 559 e = next; 560 } 561 } 562 } 563 564 /** 565 * Copies all of the mappings from the specified map to this map. 566 * These mappings will replace any mappings that this map had for any 567 * of the keys currently in the specified map. 568 * 569 * @param m mappings to be stored in this map. 570 * @throws NullPointerException if the specified map is null. 571 */ 572 public void putAll(Map<? extends K, ? extends V> m) { 573 int numKeysToBeAdded = m.size(); 574 if (numKeysToBeAdded == 0) 575 return; 576 577 /* 578 * Expand the map if the map if the number of mappings to be added 579 * is greater than or equal to threshold. This is conservative; the 580 * obvious condition is (m.size() + size) >= threshold, but this 581 * condition could result in a map with twice the appropriate capacity, 582 * if the keys to be added overlap with the keys already in this map. 583 * By using the conservative calculation, we subject ourself 584 * to at most one extra resize. 585 */ 586 if (numKeysToBeAdded > threshold) { 587 int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1); 588 if (targetCapacity > MAXIMUM_CAPACITY) 589 targetCapacity = MAXIMUM_CAPACITY; 590 int newCapacity = table.length; 591 while (newCapacity < targetCapacity) 592 newCapacity <<= 1; 593 if (newCapacity > table.length) 594 resize(newCapacity); 595 } 596 597 for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) 598 put(e.getKey(), e.getValue()); 599 } 600 601 /** 602 * Removes the mapping for a key from this weak hash map if it is present. 603 * More formally, if this map contains a mapping from key <tt>k</tt> to 604 * value <tt>v</tt> such that <code>(key==null ? k==null : 605 * key.equals(k))</code>, that mapping is removed. (The map can contain 606 * at most one such mapping.) 607 * 608 * <p>Returns the value to which this map previously associated the key, 609 * or <tt>null</tt> if the map contained no mapping for the key. A 610 * return value of <tt>null</tt> does not <i>necessarily</i> indicate 611 * that the map contained no mapping for the key; it's also possible 612 * that the map explicitly mapped the key to <tt>null</tt>. 613 * 614 * <p>The map will not contain a mapping for the specified key once the 615 * call returns. 616 * 617 * @param key key whose mapping is to be removed from the map 618 * @return the previous value associated with <tt>key</tt>, or 619 * <tt>null</tt> if there was no mapping for <tt>key</tt> 620 */ 621 public V remove(Object key) { 622 Object k = maskNull(key); 623 int h = hash(k); 624 Entry<K,V>[] tab = getTable(); 625 int i = indexFor(h, tab.length); 626 Entry<K,V> prev = tab[i]; 627 Entry<K,V> e = prev; 628 629 while (e != null) { 630 Entry<K,V> next = e.next; 631 if (h == e.hash && eq(k, e.get())) { 632 modCount++; 633 size--; 634 if (prev == e) 635 tab[i] = next; 636 else 637 prev.next = next; 638 return e.value; 639 } 640 prev = e; 641 e = next; 642 } 643 644 return null; 645 } 646 647 /** Special version of remove needed by Entry set */ 648 boolean removeMapping(Object o) { 649 if (!(o instanceof Map.Entry)) 650 return false; 651 Entry<K,V>[] tab = getTable(); 652 Map.Entry<?,?> entry = (Map.Entry<?,?>)o; 653 Object k = maskNull(entry.getKey()); 654 int h = hash(k); 655 int i = indexFor(h, tab.length); 656 Entry<K,V> prev = tab[i]; 657 Entry<K,V> e = prev; 658 659 while (e != null) { 660 Entry<K,V> next = e.next; 661 if (h == e.hash && e.equals(entry)) { 662 modCount++; 663 size--; 664 if (prev == e) 665 tab[i] = next; 666 else 667 prev.next = next; 668 return true; 669 } 670 prev = e; 671 e = next; 672 } 673 674 return false; 675 } 676 677 /** 678 * Removes all of the mappings from this map. 679 * The map will be empty after this call returns. 680 */ 681 public void clear() { 682 // clear out ref queue. We don't need to expunge entries 683 // since table is getting cleared. 684 while (queue.poll() != null) 685 ; 686 687 modCount++; 688 Arrays.fill(table, null); 689 size = 0; 690 691 // Allocation of array may have caused GC, which may have caused 692 // additional entries to go stale. Removing these entries from the 693 // reference queue will make them eligible for reclamation. 694 while (queue.poll() != null) 695 ; 696 } 697 698 /** 699 * Returns <tt>true</tt> if this map maps one or more keys to the 700 * specified value. 701 * 702 * @param value value whose presence in this map is to be tested 703 * @return <tt>true</tt> if this map maps one or more keys to the 704 * specified value 705 */ 706 public boolean containsValue(Object value) { 707 if (value==null) 708 return containsNullValue(); 709 710 Entry<K,V>[] tab = getTable(); 711 for (int i = tab.length; i-- > 0;) 712 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 713 if (value.equals(e.value)) 714 return true; 715 return false; 716 } 717 718 /** 719 * Special-case code for containsValue with null argument 720 */ 721 private boolean containsNullValue() { 722 Entry<K,V>[] tab = getTable(); 723 for (int i = tab.length; i-- > 0;) 724 for (Entry<K,V> e = tab[i]; e != null; e = e.next) 725 if (e.value==null) 726 return true; 727 return false; 728 } 729 730 /** 731 * The entries in this hash table extend WeakReference, using its main ref 732 * field as the key. 733 */ 734 private static class Entry<K,V> extends WeakReference<Object> implements Map.Entry<K,V> { 735 V value; 736 final int hash; 737 Entry<K,V> next; 738 739 /** 740 * Creates new entry. 741 */ 742 Entry(Object key, V value, 743 ReferenceQueue<Object> queue, 744 int hash, Entry<K,V> next) { 745 super(key, queue); 746 this.value = value; 747 this.hash = hash; 748 this.next = next; 749 } 750 751 @SuppressWarnings("unchecked") 752 public K getKey() { 753 return (K) WeakHashMap.unmaskNull(get()); 754 } 755 756 public V getValue() { 757 return value; 758 } 759 760 public V setValue(V newValue) { 761 V oldValue = value; 762 value = newValue; 763 return oldValue; 764 } 765 766 public boolean equals(Object o) { 767 if (!(o instanceof Map.Entry)) 768 return false; 769 Map.Entry<?,?> e = (Map.Entry<?,?>)o; 770 K k1 = getKey(); 771 Object k2 = e.getKey(); 772 if (k1 == k2 || (k1 != null && k1.equals(k2))) { 773 V v1 = getValue(); 774 Object v2 = e.getValue(); 775 if (v1 == v2 || (v1 != null && v1.equals(v2))) 776 return true; 777 } 778 return false; 779 } 780 781 public int hashCode() { 782 K k = getKey(); 783 V v = getValue(); 784 return ((k==null ? 0 : k.hashCode()) ^ 785 (v==null ? 0 : v.hashCode())); 786 } 787 788 public String toString() { 789 return getKey() + "=" + getValue(); 790 } 791 } 792 793 private abstract class HashIterator<T> implements Iterator<T> { 794 private int index; 795 private Entry<K,V> entry = null; 796 private Entry<K,V> lastReturned = null; 797 private int expectedModCount = modCount; 798 799 /** 800 * Strong reference needed to avoid disappearance of key 801 * between hasNext and next 802 */ 803 private Object nextKey = null; 804 805 /** 806 * Strong reference needed to avoid disappearance of key 807 * between nextEntry() and any use of the entry 808 */ 809 private Object currentKey = null; 810 811 HashIterator() { 812 index = isEmpty() ? 0 : table.length; 813 } 814 815 public boolean hasNext() { 816 Entry<K,V>[] t = table; 817 818 while (nextKey == null) { 819 Entry<K,V> e = entry; 820 int i = index; 821 while (e == null && i > 0) 822 e = t[--i]; 823 entry = e; 824 index = i; 825 if (e == null) { 826 currentKey = null; 827 return false; 828 } 829 nextKey = e.get(); // hold on to key in strong ref 830 if (nextKey == null) 831 entry = entry.next; 832 } 833 return true; 834 } 835 836 /** The common parts of next() across different types of iterators */ 837 protected Entry<K,V> nextEntry() { 838 if (modCount != expectedModCount) 839 throw new ConcurrentModificationException(); 840 if (nextKey == null && !hasNext()) 841 throw new NoSuchElementException(); 842 843 lastReturned = entry; 844 entry = entry.next; 845 currentKey = nextKey; 846 nextKey = null; 847 return lastReturned; 848 } 849 850 public void remove() { 851 if (lastReturned == null) 852 throw new IllegalStateException(); 853 if (modCount != expectedModCount) 854 throw new ConcurrentModificationException(); 855 856 WeakHashMap.this.remove(currentKey); 857 expectedModCount = modCount; 858 lastReturned = null; 859 currentKey = null; 860 } 861 862 } 863 864 private class ValueIterator extends HashIterator<V> { 865 public V next() { 866 return nextEntry().value; 867 } 868 } 869 870 private class KeyIterator extends HashIterator<K> { 871 public K next() { 872 return nextEntry().getKey(); 873 } 874 } 875 876 private class EntryIterator extends HashIterator<Map.Entry<K,V>> { 877 public Map.Entry<K,V> next() { 878 return nextEntry(); 879 } 880 } 881 882 // Views 883 884 private transient Set<Map.Entry<K,V>> entrySet = null; 885 886 /** 887 * Returns a {@link Set} view of the keys contained in this map. 888 * The set is backed by the map, so changes to the map are 889 * reflected in the set, and vice-versa. If the map is modified 890 * while an iteration over the set is in progress (except through 891 * the iterator's own <tt>remove</tt> operation), the results of 892 * the iteration are undefined. The set supports element removal, 893 * which removes the corresponding mapping from the map, via the 894 * <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, 895 * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> 896 * operations. It does not support the <tt>add</tt> or <tt>addAll</tt> 897 * operations. 898 */ 899 public Set<K> keySet() { 900 Set<K> ks = keySet; 901 return (ks != null ? ks : (keySet = new KeySet())); 902 } 903 904 private class KeySet extends AbstractSet<K> { 905 public Iterator<K> iterator() { 906 return new KeyIterator(); 907 } 908 909 public int size() { 910 return WeakHashMap.this.size(); 911 } 912 913 public boolean contains(Object o) { 914 return containsKey(o); 915 } 916 917 public boolean remove(Object o) { 918 if (containsKey(o)) { 919 WeakHashMap.this.remove(o); 920 return true; 921 } 922 else 923 return false; 924 } 925 926 public void clear() { 927 WeakHashMap.this.clear(); 928 } 929 930 public Spliterator<K> spliterator() { 931 return new KeySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 932 } 933 } 934 935 /** 936 * Returns a {@link Collection} view of the values contained in this map. 937 * The collection is backed by the map, so changes to the map are 938 * reflected in the collection, and vice-versa. If the map is 939 * modified while an iteration over the collection is in progress 940 * (except through the iterator's own <tt>remove</tt> operation), 941 * the results of the iteration are undefined. The collection 942 * supports element removal, which removes the corresponding 943 * mapping from the map, via the <tt>Iterator.remove</tt>, 944 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, 945 * <tt>retainAll</tt> and <tt>clear</tt> operations. It does not 946 * support the <tt>add</tt> or <tt>addAll</tt> operations. 947 */ 948 public Collection<V> values() { 949 Collection<V> vs = values; 950 return (vs != null) ? vs : (values = new Values()); 951 } 952 953 private class Values extends AbstractCollection<V> { 954 public Iterator<V> iterator() { 955 return new ValueIterator(); 956 } 957 958 public int size() { 959 return WeakHashMap.this.size(); 960 } 961 962 public boolean contains(Object o) { 963 return containsValue(o); 964 } 965 966 public void clear() { 967 WeakHashMap.this.clear(); 968 } 969 970 public Spliterator<V> spliterator() { 971 return new ValueSpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 972 } 973 } 974 975 /** 976 * Returns a {@link Set} view of the mappings contained in this map. 977 * The set is backed by the map, so changes to the map are 978 * reflected in the set, and vice-versa. If the map is modified 979 * while an iteration over the set is in progress (except through 980 * the iterator's own <tt>remove</tt> operation, or through the 981 * <tt>setValue</tt> operation on a map entry returned by the 982 * iterator) the results of the iteration are undefined. The set 983 * supports element removal, which removes the corresponding 984 * mapping from the map, via the <tt>Iterator.remove</tt>, 985 * <tt>Set.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt> and 986 * <tt>clear</tt> operations. It does not support the 987 * <tt>add</tt> or <tt>addAll</tt> operations. 988 */ 989 public Set<Map.Entry<K,V>> entrySet() { 990 Set<Map.Entry<K,V>> es = entrySet; 991 return es != null ? es : (entrySet = new EntrySet()); 992 } 993 994 private class EntrySet extends AbstractSet<Map.Entry<K,V>> { 995 public Iterator<Map.Entry<K,V>> iterator() { 996 return new EntryIterator(); 997 } 998 999 public boolean contains(Object o) { 1000 if (!(o instanceof Map.Entry)) 1001 return false; 1002 Map.Entry<?,?> e = (Map.Entry<?,?>)o; 1003 Entry<K,V> candidate = getEntry(e.getKey()); 1004 return candidate != null && candidate.equals(e); 1005 } 1006 1007 public boolean remove(Object o) { 1008 return removeMapping(o); 1009 } 1010 1011 public int size() { 1012 return WeakHashMap.this.size(); 1013 } 1014 1015 public void clear() { 1016 WeakHashMap.this.clear(); 1017 } 1018 1019 private List<Map.Entry<K,V>> deepCopy() { 1020 List<Map.Entry<K,V>> list = new ArrayList<>(size()); 1021 for (Map.Entry<K,V> e : this) 1022 list.add(new AbstractMap.SimpleEntry<>(e)); 1023 return list; 1024 } 1025 1026 public Object[] toArray() { 1027 return deepCopy().toArray(); 1028 } 1029 1030 public <T> T[] toArray(T[] a) { 1031 return deepCopy().toArray(a); 1032 } 1033 1034 public Spliterator<Map.Entry<K,V>> spliterator() { 1035 return new EntrySpliterator<>(WeakHashMap.this, 0, -1, 0, 0); 1036 } 1037 } 1038 1039 /** 1040 * Similar form as other hash Spliterators, but skips dead 1041 * elements. 1042 */ 1043 static class WeakHashMapSpliterator<K,V> { 1044 final WeakHashMap<K,V> map; 1045 WeakHashMap.Entry<K,V> current; // current node 1046 int index; // current index, modified on advance/split 1047 int fence; // -1 until first use; then one past last index 1048 int est; // size estimate 1049 int expectedModCount; // for comodification checks 1050 1051 WeakHashMapSpliterator(WeakHashMap<K,V> m, int origin, 1052 int fence, int est, 1053 int expectedModCount) { 1054 this.map = m; 1055 this.index = origin; 1056 this.fence = fence; 1057 this.est = est; 1058 this.expectedModCount = expectedModCount; 1059 } 1060 1061 final int getFence() { // initialize fence and size on first use 1062 int hi; 1063 if ((hi = fence) < 0) { 1064 WeakHashMap<K,V> m = map; 1065 est = m.size(); 1066 expectedModCount = m.modCount; 1067 hi = fence = m.table.length; 1068 } 1069 return hi; 1070 } 1071 1072 public final long estimateSize() { 1073 getFence(); // force init 1074 return (long) est; 1075 } 1076 } 1077 1078 static final class KeySpliterator<K,V> 1079 extends WeakHashMapSpliterator<K,V> 1080 implements Spliterator<K> { 1081 KeySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1082 int expectedModCount) { 1083 super(m, origin, fence, est, expectedModCount); 1084 } 1085 1086 public KeySpliterator<K,V> trySplit() { 1087 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1088 return (lo >= mid) ? null : 1089 new KeySpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1090 expectedModCount); 1091 } 1092 1093 public void forEachRemaining(Consumer<? super K> action) { 1094 int i, hi, mc; 1095 if (action == null) 1096 throw new NullPointerException(); 1097 WeakHashMap<K,V> m = map; 1098 WeakHashMap.Entry<K,V>[] tab = m.table; 1099 if ((hi = fence) < 0) { 1100 mc = expectedModCount = m.modCount; 1101 hi = fence = tab.length; 1102 } 1103 else 1104 mc = expectedModCount; 1105 if (tab.length >= hi && (i = index) >= 0 && 1106 (i < (index = hi) || current != null)) { 1107 WeakHashMap.Entry<K,V> p = current; 1108 current = null; // exhaust 1109 do { 1110 if (p == null) 1111 p = tab[i++]; 1112 else { 1113 Object x = p.get(); 1114 p = p.next; 1115 if (x != null) { 1116 @SuppressWarnings("unchecked") K k = 1117 (K) WeakHashMap.unmaskNull(x); 1118 action.accept(k); 1119 } 1120 } 1121 } while (p != null || i < hi); 1122 } 1123 if (m.modCount != mc) 1124 throw new ConcurrentModificationException(); 1125 } 1126 1127 public boolean tryAdvance(Consumer<? super K> action) { 1128 int hi; 1129 if (action == null) 1130 throw new NullPointerException(); 1131 WeakHashMap.Entry<K,V>[] tab = map.table; 1132 if (tab.length >= (hi = getFence()) && index >= 0) { 1133 while (current != null || index < hi) { 1134 if (current == null) 1135 current = tab[index++]; 1136 else { 1137 Object x = current.get(); 1138 current = current.next; 1139 if (x != null) { 1140 @SuppressWarnings("unchecked") K k = 1141 (K) WeakHashMap.unmaskNull(x); 1142 action.accept(k); 1143 if (map.modCount != expectedModCount) 1144 throw new ConcurrentModificationException(); 1145 return true; 1146 } 1147 } 1148 } 1149 } 1150 return false; 1151 } 1152 1153 public int characteristics() { 1154 return Spliterator.DISTINCT; 1155 } 1156 } 1157 1158 static final class ValueSpliterator<K,V> 1159 extends WeakHashMapSpliterator<K,V> 1160 implements Spliterator<V> { 1161 ValueSpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1162 int expectedModCount) { 1163 super(m, origin, fence, est, expectedModCount); 1164 } 1165 1166 public ValueSpliterator<K,V> trySplit() { 1167 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1168 return (lo >= mid) ? null : 1169 new ValueSpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1170 expectedModCount); 1171 } 1172 1173 public void forEachRemaining(Consumer<? super V> action) { 1174 int i, hi, mc; 1175 if (action == null) 1176 throw new NullPointerException(); 1177 WeakHashMap<K,V> m = map; 1178 WeakHashMap.Entry<K,V>[] tab = m.table; 1179 if ((hi = fence) < 0) { 1180 mc = expectedModCount = m.modCount; 1181 hi = fence = tab.length; 1182 } 1183 else 1184 mc = expectedModCount; 1185 if (tab.length >= hi && (i = index) >= 0 && 1186 (i < (index = hi) || current != null)) { 1187 WeakHashMap.Entry<K,V> p = current; 1188 current = null; // exhaust 1189 do { 1190 if (p == null) 1191 p = tab[i++]; 1192 else { 1193 Object x = p.get(); 1194 V v = p.value; 1195 p = p.next; 1196 if (x != null) 1197 action.accept(v); 1198 } 1199 } while (p != null || i < hi); 1200 } 1201 if (m.modCount != mc) 1202 throw new ConcurrentModificationException(); 1203 } 1204 1205 public boolean tryAdvance(Consumer<? super V> action) { 1206 int hi; 1207 if (action == null) 1208 throw new NullPointerException(); 1209 WeakHashMap.Entry<K,V>[] tab = map.table; 1210 if (tab.length >= (hi = getFence()) && index >= 0) { 1211 while (current != null || index < hi) { 1212 if (current == null) 1213 current = tab[index++]; 1214 else { 1215 Object x = current.get(); 1216 V v = current.value; 1217 current = current.next; 1218 if (x != null) { 1219 action.accept(v); 1220 if (map.modCount != expectedModCount) 1221 throw new ConcurrentModificationException(); 1222 return true; 1223 } 1224 } 1225 } 1226 } 1227 return false; 1228 } 1229 1230 public int characteristics() { 1231 return 0; 1232 } 1233 } 1234 1235 static final class EntrySpliterator<K,V> 1236 extends WeakHashMapSpliterator<K,V> 1237 implements Spliterator<Map.Entry<K,V>> { 1238 EntrySpliterator(WeakHashMap<K,V> m, int origin, int fence, int est, 1239 int expectedModCount) { 1240 super(m, origin, fence, est, expectedModCount); 1241 } 1242 1243 public EntrySpliterator<K,V> trySplit() { 1244 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; 1245 return (lo >= mid) ? null : 1246 new EntrySpliterator<K,V>(map, lo, index = mid, est >>>= 1, 1247 expectedModCount); 1248 } 1249 1250 1251 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { 1252 int i, hi, mc; 1253 if (action == null) 1254 throw new NullPointerException(); 1255 WeakHashMap<K,V> m = map; 1256 WeakHashMap.Entry<K,V>[] tab = m.table; 1257 if ((hi = fence) < 0) { 1258 mc = expectedModCount = m.modCount; 1259 hi = fence = tab.length; 1260 } 1261 else 1262 mc = expectedModCount; 1263 if (tab.length >= hi && (i = index) >= 0 && 1264 (i < (index = hi) || current != null)) { 1265 WeakHashMap.Entry<K,V> p = current; 1266 current = null; // exhaust 1267 do { 1268 if (p == null) 1269 p = tab[i++]; 1270 else { 1271 Object x = p.get(); 1272 V v = p.value; 1273 p = p.next; 1274 if (x != null) { 1275 @SuppressWarnings("unchecked") K k = 1276 (K) WeakHashMap.unmaskNull(x); 1277 action.accept 1278 (new AbstractMap.SimpleImmutableEntry<K,V>(k, v)); 1279 } 1280 } 1281 } while (p != null || i < hi); 1282 } 1283 if (m.modCount != mc) 1284 throw new ConcurrentModificationException(); 1285 } 1286 1287 public boolean tryAdvance(Consumer<? super Map.Entry<K,V>> action) { 1288 int hi; 1289 if (action == null) 1290 throw new NullPointerException(); 1291 WeakHashMap.Entry<K,V>[] tab = map.table; 1292 if (tab.length >= (hi = getFence()) && index >= 0) { 1293 while (current != null || index < hi) { 1294 if (current == null) 1295 current = tab[index++]; 1296 else { 1297 Object x = current.get(); 1298 V v = current.value; 1299 current = current.next; 1300 if (x != null) { 1301 @SuppressWarnings("unchecked") K k = 1302 (K) WeakHashMap.unmaskNull(x); 1303 action.accept 1304 (new AbstractMap.SimpleImmutableEntry<K,V>(k, v)); 1305 if (map.modCount != expectedModCount) 1306 throw new ConcurrentModificationException(); 1307 return true; 1308 } 1309 } 1310 } 1311 } 1312 return false; 1313 } 1314 1315 public int characteristics() { 1316 return Spliterator.DISTINCT; 1317 } 1318 } 1319 1320 }